A key objective of phosphoproteomic analyses is to obtain an in-depth understanding of protein phosphorylation and signaling networks in cells. However, despite the great progress that has been made over the past few years, our ability to analyze such signaling pathways is still greatly limited by a number of serious technical challenges. The long term goal is to develop novel proteomics strategies valuable for understanding on the molecular level the role of phosphorylation in regulating cell proliferation. The objective in this application is to devise and optimize effective and efficient methodologies and strategies for the analyses of tyrosine kinase phosphoproteomes, using a dual functional tyrosine kinase Syk as the model system. This approach will utilize functional, soluble polymers for the efficient and inclusive isolation of phosphopeptides coupled with an integrated chemical, mass spectrometric, and computational strategy for the identification of specific tyrosine kinase substrates and for quantitative phosphoproteomics. We will focus on Syk-dependent signaling and establish protocols that will ultimately provide a powerful method to dissect any signaling pathway regulated by protein-tyrosine phosphorylation. Guided by strong preliminary data, this objective will be achieved by pursuing three specific aims: 1) Develop a proteomic platform for the analysis of protein phosphorylation. We will primarily develop, characterize and optimize functionalized soluble polymers designed for the affinity and chemical isolation of phosphopeptides; 2) Identification of specific tyrosine-kinase substrates and their phosphorylation sites; and 3) In-depth analyses of tyrosine kinase phosphoproteomes in several cancer types. We will develop and apply our quantitative proteomic technologies for the identification and quantification of tyrosine-phosphorylation sites in several cancer types. This project is innovative because it will develop a series of novel analytical techniques to directly identify novel tyrosine kinase substrates and phosphorylation sites that will provide investigators with a significantly expanded capability to dissect signaling pathways. The developed techniques will provide detailed knowledge at the molecular level on precisely how tyrosine kinases are involved in cell signaling under different physiological conditions through dynamic changes in protein phosphorylation. It is also expected that, by identifying a kinase's direct substrates, the proposed research will provide a powerful tool to conveniently map kinase networks.